The present invention relates to a device for frothing and heating liquids, such as milk and the like, in particular for automatic machines, which is provided with longitudinal channels for suction of the liquid-frothing air.
In order to make milk-based hot drinks, such as cappuccino and the like, use is made of steam-producing machines, by means of which the milk necessary for preparation of the drink is heated and frothed with air, so as to obtain a surface foam which is quite liked by consumers.
For this purpose the machines of the known type comprise automatically operating steam heating and frothing devices provided with mixing chambers which have a complex configuration and narrow flow cross-sections and are also equipped with members for micrometric adjustment of the cross-sections themselves, which are difficult to manufacture and difficult to clean as well as being subject, during use, to the formation of milk deposits which alter the values of the preselected cross-sections, resulting in irregular operation of the assembly.
In addition to these types of devices, a device for frothing and heating milk for drinks is also known from EP 0,344,859 in the name of the present Applicant, said device comprising a substantially tubular cylindrical body connected to the steam-emitting pipe of a machine for preparing hot drinks, which cylindrical body has inside it a first nozzle, outside of which there is defined, inside the cylindrical body, a chamber in which there emerges a duct for the suction of milk from a container, the said nozzle being located above a constriction extended downwards until it emerges in an extension of the said cylindrical body forming a second nozzle outside of which, inside the cylindrical body, there is defined an annular chamber provided with one or more radial openings communicating with the exterior and an axial passage which places in communication the chamber with the bottom part of the cylindrical body, the second nozzle being placed in communication with the chamber by means of radial holes, through which the frothing air is sucked.
These devices of the known type have the drawback, however, arising from the fact that, in the case of liquids to be frothed such as milk and the like which have a high density and contain a high percentage of fatty substances, the holes for drawing air from the outside, which are formed radially in the vicinity of the frothing chamber, tend to get blocked up by the milk which tends to bubble out owing to the effect of the pressures existing inside the frothing chamber; in fact, said milk which comes into contact with the air intake hole leaves fatty deposits on the hole itself which tends to become blocked, gradually reducing the quantity of air sucked in until the desired frothing action no longer occurs.
In addition, as a result of these outflows of milk, it is necessary to perform frequent cleaning operations both in order to unblock the suction hole and so as to avoid stagnation of fatty substances on the outside of the frothing device, which stagnation may give rise to unhygienic fermentation phenomena.
The technical problem which is posed, therefore, is that of providing a device for frothing and heating liquids such as milk and the like, which is provided with means for suction of the air from the outside designed not to come into contact with the liquid to be frothed, thus making it possible to maintain unaltered, over time, the quantity of air sucked in for frothing and avoid the troublesome external outflow of liquid from said suction channels.
Within the scope of this technical problem a further necessity is that the device should be formed by a reduced number of parts which can be easily assembled and which have a low cost and can be easily washed internally without the need for disassembly thereof.